This invention relates to a pulley having a high-friction circumferential groove for receiving a friction-belt therein and a manufacturing method therefor.
FIGS. 1 to 4 illustrates one example of conventional steps for manufacturing a conventional pulley for use with a friction belt. The illustrated pulley is the one for the alternator for use in a vehicle. According to the conventional manufacturing method, as shown in FIG. 1, a solid, drum-shaped piece of a forgeable steel blank material 1 is prepared. This solid blank material 1 is first cold forged into a cup-shaped material 2 with a first flange 3 at the bottom of it as shown in FIG. 2. Then the cup-shaped material 2 is again cold forged into a cup 4 with a second flange 5 at the open edge of the cylindrical wall of the cup 4. It is seen that the a cylindrical surface 6 in which circumferential grooves for receiving friction belts (not shown) such as V-belts are formed is defined between the first and the second flanges 3 and 5. A central bore 7 is also formed at this stage. Thus, a basic pulley configuration is obtained at this stage. Finally, as shown in FIG. 4, circumferential grooves 8 for receiving friction belts (not shown) therein are formed in the cylindrical surface 6 between the first and the second flanges 3 and 5 to obtain a finished pulley 9. The circumferential grooves 8 are usually V-grooves as shown in FIG. 4. Such pulley 9 can be used in a vehicular alternator together with a V-belt (not shown) with a plurality of V-grooves.
However, since the circumferential grooves 8 in the pulley 9 are formed by rolling, they have groove surfaces which are very smooth. Therefore, the coefficient of friction of the groove surfaces of the grooves 8 relative to the friction belt is very low, often causing a slippage between the pulley 9 and the belt on it.